The present invention relates generally to safety restraint systems for motor vehicles. More specifically, the present invention is directed to a safety belt retractor having an energy management mechanism capable of transferring energy to the retractor during a collision and a mode shifting mechanism capable of subsequently disabling the retractor when the amount of energy absorbed by the energy management mechanism exceeds a maximum allowable limit.
As part of the occupant restraint system currently used in motor vehicles, several different types of safety belt retractors are available which provide enhanced occupant comfort and/or different functional modes. For example, one type of safety belt retractor, often referred to as an emergency locking retractor (ELR), includes a latch mechanism which is automatically actuated in response to certain high acceleration conditions to prevent payout of the safety belt. Typically the latch mechanism is actuated by an inertia-sensitive actuator when the vehicle is subjected to a certain deceleration level and/or actuated by a web-sensitive actuator when the belt is withdrawn from the spool at a rate exceeding a designated level. Another type of safety belt retractor, commonly referred to as an automatic locking retractor (ALR), includes a latch mechanism which is selectively actuated by withdrawing a predetermined length of the safety belt. Once the predetermined length of the safety belt has been withdrawn, the latch mechanism allows retraction but prevents further payout of the safety belt. Thereafter, this automatic locking function is canceled in response to the retraction of a predetermined amount of the safety belt to its stowed position. As a further variation, some dual-mode safety belt retractors normally operate as an ELR retractor and can be selectively switch to operate as an ALR retractor such as, for example, when it is desired to secure a portable child seat to the vehicle seat. These retractors are often referred to as ELR/ALR retractors.
These different safety belt retractors may also include an energy management mechanism which functions to absorb a portion of the energy (i.e. impact loads) transferred from the safety belt to the seat occupant during a collision. For example, some energy management retractors include a torsion bar having a first end fixed to the spool. During a collision, the latch mechanism engages the second end of the torsion bar. As such, the impact force applied by the seat occupant to the safety belt is transferred to the spool and causes the torsion bar to twist relative to the latched second end. Such torsional yielding of the torsion bar results in a limited though controlled amount of additional rotation of the spool which, in turn, permits a corresponding amount of additional belt to be withdrawn from the retractor. The controlled payout of additional belt in response to loading on the safety belt effectively dampens the amount of impact energy transferred to the seat occupant and controls the forward motion of the occupant. The physical dimensions and material characteristics of the torsion bar are selected to define its yield rate and permit it to rotate a predetermined number of turns. More specifically, this predetermined number of turns is selected to be greater than that required for the torsion bar to survive a single severe collision or the cumulative effect of a number of less severe collisions.
An object of the present invention is to provide a safety belt retractor having an energy management mechanism capable of transferring a portion of the impact energy to the retractor during one or more collisions and a mode shifting mechanism capable of determining the severity of the collision(s) as a function of the amount of energy absorbed by the energy management mechanism.
Another object of the present invention is to provide the mode shifting mechanism with the capability to disable the safety belt retractor when the amount of energy absorbed by the energy management mechanism exceeds a maximum allowable limit.
A further object of the present invention is to integrate the mode shifting mechanism into the automatic locking mechanism of an emergency locking retractor.
Accordingly, the present invention is directed to a safety belt retractor comprising a spool, a belt wound on the spool, a ratchet wheel, and an emergency locking mechanism normally operable in a released mode to permit payout and retraction of the belt and which is automatically shifted into a locked mode for locking the ratchet wheel against rotation to prevent payout of the belt in response to the occurrence of a predetermined acceleration condition. The safety belt retractor also includes an energy management mechanism connecting the ratchet wheel to the spool and which is adapted to yield in response to occupant loading exerted on the belt when ratchet wheel is locked against rotation, and a mode shifting mechanism which is normally operable in a non-activated mode to permit operation of the emergency locking mechanism. The mode shifting mechanism is automatically shifted into a lock-out mode in response to the belt being wound on the spool when the loading exerted by the belt on the energy management mechanism causes it to yield in excess of a maximum allowable limit for locking the ratchet wheel against rotation to prevent payout of the belt.